The invention relates to an aftertreatment apparatus, incorporating a heat station, for printing plates which have been exposed imagewise through an original.
To restore the sensitivity of photopolymerizable copying materials which have been deposited as a photosensitive layer on a printing plate substrate and whose sensitivity has decreased through absorption of molecular oxygen, it is known from DE-B 1,214,085 (U.S. Pat. No. 3,144,331) to expose the photosensitive layer by means of 70 to 98% of the radiation quantity of an actinic radiation which would be necessary to initiate photopolymerization with uniform incidence. The exposure is carried out through, for example, the transparent printing plate substrate, with an actinic radiation being used which has a wavelength such that only 10 to 70% of the radiation is absorbed by the photopolymerizable layer. In this process, exposure is carried out once diffusely and once imagewise. The diffuse or pre-exposure is carried out with a lower intensity, namely with 70 to 98% of the radiation intensity which is necessary to achieve the complete exposure action. This pre-exposure is then followed by the imagewise exposure through an original: employing the full radiation intensity.
U.S. Pat. No. 4,298,803 discloses a process in which a photoresist layer is pre-exposed with an intensity which is lower than the critical exposure intensity at which the photoresist is completely decomposed at a particular point. After this pre-exposure, the photoresist layer is exposed imagewise. The sequence of the pre-exposure and the exposure through an original can be interchanged. In both cases, the sensitivity of the photoresist layer is improved, thereby shortening processing time considerably. In the equipment used for this process, both the imagewise exposure and the pre-exposure or after-exposure of the photoresist can be carried out by means of an electron beam, or a UV or X-ray radiation source.
U.S. Pat. No. 4,716,097 likewise discloses a process in which a photopolymeric layer which contains a dyestuff is first exposed diffusely by means of light of a wavelength above 400 nm and an intensity of at least 1,500 lumen/m.sup.2, and then exposed imagewise.
German Offenlegungsschrift DE-A 2,412,571 describes a process for curing a photocurable polymer layer of a printing plate, in which process exposure is first carried out diffusely for a short time and then imagewise until the polymer layer is virtually completely cured in the exposed regions. The diffuse exposure time is not more than 90% of the time during which the complete curing of the polymer layer takes place at the same intensity of radiation both for the pre-exposure and a-so for the imagewise exposure.